The present invention relates to precision rocker mills of the type which produce tubes from hollow metal workpieces.
A rocker mill of that type is disclosed for example in Kondoh U.S. Pat. No. 4,562,713 and in copending U.S. application Ser. No. 297,431 filed Jan. 17 1989 U.S. Pat. No. 4,930,328. Such mills typically include a movable rollstand which is reciprocated along a hollow workpiece. The rollstand includes a pair of grooved roll dies which define a nip through which the workpiece is passed so as to be radially compressed. A mandrel is disposed within the workpiece to radially support the inside of the workpiece. The workpiece is progressively advanced and rotated as the rollstand is reciprocated therealong.
The grooves of the roll dies are of progressively narrowing width in the circumferential direction. Thus, by rotating the roll dies, the workpiece is subjected to a progressively increasing radial compression whereby the diameter of the workpiece is progressively reduced.
In practice, when a rolling operation has ended it is occasionally necessary to replace the roll dies, e.g., after they have become worn or are to be replaced by roll dies having differently sized grooves. Heretofore, the roll die replacement operation has involved appreciable time and difficulty. For example, considerable disassembly of parts is performed while the rollstand remains in the mill, a practice which can result in considerable downtime of the machine. It has been known to lift the rollstand from the mill, but this requires the need to provide an overhead crane, or the like, which is cumbersome and expensive. Also, conventional roll dies are mounted on parallel steel arbors which themselves are mounted in bearings within the rollstand. Spur gears are coaxially attached to the arbors on one side of the rollstand so as to be in meshing engagement, and a pinion gear is coaxially attached to one of the arbors at an opposite side of the rollstand. The pinion gear meshes with a toothed rack whereby relative movement between the rack and pinion gear causes the pinion gear to rotate. The spur gear which is coaxially attached to the pinion gear is thus rotated and causes the other spur gear to rotate as well. Consequently, the arbors and roll dies are rotated in unison. It will be appreciated that replacement of the roll dies involves the need to remove the spur gears, thereby lengthening the down time of the mill.
As an alternative arrangement, the spur gears can be eliminated and instead two pinion gears are disposed on opposite sides of the roller mill and are arranged to mesh with respective racks. However, such an arrangement presents even more difficulty in removing the roll dies since there is always a rack in the way.
Furthermore, the roll dies are typically mounted to the arbors by a heat-shrinking operation. Thus, in order to replace the roll dies it has been necessary to take the roll die/arbor units to a heat-treatment facility.
In addition, the presence of the spur gears complicates the process of adjusting the vertical relationship of the roll dies. Such adjustment is typically made in repeated steps during a rolling operation. That is, after the workpiece has been subjected to one or more rolling strokes, the machine is stopped and an operator measures the diameter of the workpiece to determine whether the roll dies are properly spaced apart. This procedure is performed repeatedly before a position of final adjustment can be achieved. The measuring of the workpiece is performed at the nip zone of the roll dies, requiring that the operator reach around an end of the rollstand. Due to the confined nature of the space within the mill housing in which the rollstand is located, it is difficult to perform this measuring step, the difficulty being aggravated by the presence of the spur gears.